66 



CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC. 



to a small rubber tubing and to the mercury manometer D, which also 

 serves as a valve for passing a given amount of air through a series of 

 U -tubes for analysis of the air from time to time. It is assumed that the 

 air drawn at the point H is of substantially the same composition as that 

 inside the chamber, an assumption that may not be strictly true, but doubt- 

 less the sample thus obtained is constantly proportional to the average 

 composition, which fluctuates but slowly. Ordinarily the piping leading 

 from the left-hand arm of the tube D is left open to the air and conse- 



Fig. 30. — Diagram of absorber table. 1 and 2 contain sulphuric acid; K contains 

 potash-lime; G, sodium bicarbonate can; F, rotary blower for maintaining air- 

 current; H, valves for closing either side; and D, mercury manometer and 

 valve for diverting air to U -tubes on table. Air leaves A, passes through the 

 meter, and then through drying tower B and through C to ingoing air-pipe. 

 At the left is the regulating rheostat and motor and snap-switch. General 

 direction of ventilation is indicated by arrows. 



quently the difference in the level of the mercury in the two arms of D 

 indicates the pressure on the system. This is ordinarily not far from 40 to 

 50 millimeters of mercury. 



The absorber table, with the U -tubes and meter for residual analyses, is 

 shown in the foreground in fig. 2. The two white porcelain vessels with a 

 silver-plated can between them are on the middle shelf. The sodium bicar- 

 bonate can, for removing traces of acid fumes, is connected in an upright 



